The invention concerns a satellite in terrestrial orbit whose attitude is stabilized by rotating the satellite about its own axis (sometimes called "spin-stabilized" satellite) and is directed to minimizing the sensitivity of satellites to some causes of external disturbance.
Any satellite is acted on by external disturbing forces due to its environments. The external forces include solar radiation pressure, gravity gradient, terrestrial magnetic field, and atmospheric drag, especially in low orbit.
In a geostationary orbit the solar radiation pressure is usually the predominant disturbance.
Non-coincidence of the center of mass of the satellite and the center of application of the external forces causes torques to be exerted on the satellite.
In an environment of this kind, the satellite is generally stabilized by producing a substantial kinetic moment, either by means of the rotation of the satellite about its own axis in the case of a spin-stabilized satellite, or by means of inertia wheels designed to create a kinetic moment by artificial means in the case of a "three axis stabilized" satellite.
Nevertheless, the effect of the applied external torques modifies the characteristics of the kinetic moment and in particular its direction, so that the attitude of the satellite is subject to drift.
To meet the satellite stability constraints relating to its mission, in particular pointing of antennas or observation instruments, compensation, known as "attitude control", must be applied using appropriate actuators such as gas jet thrusters and other devices.
In the case of a spin-stabilized satellite, it is not possible to use magnetic actuators because the direction of the kinetic moment created in this way would rotate with the satellite. Only abrupt action actuators can be used for spin-stabilized satellites; in practice gas jet thrusters.
Attitude control maneuvers are then accompanied by a temporary disturbance to the nominal attitude of the satellite and, therefore, an interruption in its mission. As these maneuvers must be carried out at regular intervals, they cause frequent interruptions of the mission. Also, the generation of the gas jets used for these maneuvers consumes propellants and this reduces the total life of the satellite.
An object of the invention is to alleviate the aforementioned disadvantages in relation to a spin-stabilized satellite, in particular where the latter is in an equatorial, preferably geostationery orbit, that is to say in a situation in which the external disturbances are due primarily to the solar radiation pressure (above "low" orbits, at an altitude of typically 20,000 to 40,000 km, for example).